Sulfur dioxide, SO2, and sulfur trioxide, SO3, collectively called SOx gases, are normally formed during the combustion of fuels such as coal, coke or oil that also contain sulfur. These SOx gases are considered air pollutants, and desulfurization measures are often required to control or minimize the amounts of these gases in the flue gas streams that are released into the atmosphere. Electric utility power plants are a significant source of SOx-containing combustion flue gas or waste gas streams that require desulfurization control measures.
Sulfur dioxide is the predominant SOx component in flue gas streams from sulfur-containing oil- or coal-fired combustion facilities. Methods for removing SO2 are well known in the air pollution control field, and known flue gas desulfurization methods use calcium or sodium alkali sorbents, or combinations of these, in dry injection, semi-dry injection or wet scrubbing operations. Currently preferred desulfurization methods, in new high-sulfur coal-fired power plants, utilize wet scrubbing in gas-liquid contactors that use limestone or lime as the SO2-reactive desulfurization agent.
Retrofitting existing older small capacity power plants with desulfurization equipment is often limited by the lack of available room, a significant issue with the installation of wet scrubbing desulfurization equipment. Dry or semi-dry scrubbing methods may not be amenable in retrofit situations, since calcium sorbents can be detrimental to existing electrostatic precipitator performance, reaction kinetics between sulfur dioxide and calcium sorbents require long gas-solid residence times for complete reaction, or the desulfurization byproduct characteristics (e.g., solubility) may not permit inexpensive disposal in a landfill.
Techniques have been described for removing sulfur dioxide from flue gas streams using oxidants such as hydrogen peroxide, H2O2. U.S. Pat. No. 5,595,713 and No. 5,674,459, both of Gohara et al. and assigned to Babcock & Wilcox, disclose equipment systems for flue gas desulfurization. The desulfurization systems of Gohara et al. produce sulfuric acid and/or calcium sulfate as byproducts but do not address the complexity of the unit operations required to recover gypsum (calcium sulfate dihydrate) as a byproduct.
The flue gas desulfurization process of this invention efficiently removes SO2 contaminant from a flue gas stream, in a process that also economically produces gypsum as a substantially dry product.